Method and means for controlling discharge gaps



July 9, 1929.

K. ROTTGARDT ET AL METHOD AND HEARS FOR CONTROLLING DISCHARGE GAPS Filed June 4, 1924 2 Sheets-Sheet Ila 1711 437080 7'3 Karl Royardtf M70, ww/llflw f July 9, 1929.

K.- ROTTGARDT ET AL METHOD AND MEANS FOR CONTROLLING DISCHARGE GAPS Filed June 4, 1924 2 Sheets-Sheet and ZarZuJffiL/fulanu,

Patented July 9, 1929. I

UNITED STATESPATENT OFFICE.

KARL ROTT GARDT, 0F DAHLEM, NEAR BERLIN, AN D LUDWIG K'fi'HN, OF CHARLOTTE-N- BURG, NEAR BERLIN, GERMANY, ASSIGNORS 'IO DR. ERICK F. HUTH G. M.

0F BERLIN, GERMANY, A FIRM.

METHOD AND MEANS FOR CONTROLLING DISCHARGE GAPS.

Application filed June 4, 1924, Serial No. 717,833, and in Germany June 5, 1923.

The invention refers to electric discharge tubes operating with'gas ionization, or thermionic, or electron discharges which may have one or several liquid or solid cathodes for cathode ray or ion or electron emission and one or several anodes.

The invention refers to a sudden or discontinuous maintained diminution of the inner resistance of the discharge gap. This is effected by a variation of a mechanical or an electrical value influencing the discharge gap and its operating state; e. g.. by the variation of the voltage applied. or of the condition of at least one of the auxiliary electrodes in the discharge gap. or of the heating of the cathode or of a resistance overbridging a part of a discharge gap and so on. The original operating state of higher inner resistance is then again reproduced by reverting through manual or automatic operation to the electrical or mechanical values prior to the above change. The change from original state of higher inner resistance of the discharge gap to the state of reduced inner resistance and vice versa may occur periodically, and also automatically, giving in the latter case continuous oscillations.

In particular the invention consists of the fact that a part of the discharge gap is overhridged continuously or occasionally by at least one variable resistance. and that the variation of this resistance, for example its reduction, causes a sudden or discontinuous, maintained reduction of the inner resistance of the discharge gap.

The invention is more particularly described below, reference being had to some diagrammatic examples showing the principle of the invention and others showing its practical form of application.

In the drawings Fig. 1 is a diagrammatic illustration of the dependence of the anode current upon the voltage at the auxiliary electrode, as known heretofore. Figs. 2 and 3 show experimental circuits. Figs. 4 and 5 explain principles of phenomena made known by the present invention and employed thereby. Fig. 6 shows a circuit arrangement when employing the invention for generating oscillations. Fig. 7 is a diagrammatic view of the current through the discharge gap. Figs. 8 and 9 illustrate the further development of the invention in principle. Fig. 10 is a transmitter circuit for telephony.

In the first place. according to Figs. 1 to 5 the essence of the invention may be further explained on the lines of a typical example of a discharge gap, i. e., of a high vacuum glow cathode valve with grid like auxiliary electrode.

The function of such discharge gaps has according to the recent state of scientific knowledge been represented by characteristic curves illustrating the thermionic or electron current through the discharge gap depending on the grid voltage Vg and the anode voltage Va. All literature and researches referring to this subject tend to confirm the general appearance of these characteristic curves as given in Fig. 1. In this figure is shown the dependence of the anode current 13,. upon the grid voltage Vg at various anode voltages V..,, V etc. The large number of theories concerning such discharge gaps particularly when applied as amplifiers of weak alternating currents or in circuits for generating oscillations are based on such characteristic curves and on the technical ideas derived from these characteristic curves such as steepness and voltage ratio.

lVhen contemplating the family of curves shown in Fig. 1 the absolute continuity of all phenomena is evident. A continuous increase of voltage applied to the. discharge gap results in a continuous variation (increase) of the current up to the saturation value.

The invention now brings the surprising knowledge that certain phenomena are not fully defined by the above mentioned characteristic curves. The idea of the invention may be explained by the following fundamental experiment. the circuit of which is diagrammatically shown in Fig. 2.

A vacuum tube with a glow cathode k, auxiliary electrode 9 and anode a was connccted to a direct current source with the voltage Va. \Vi'th no connection between grid and anode and with an anode voltage applied. a certain current flowed, which owing to the rather closely meshed grid had a value of only a few milliamperes. A condenser was next connected between anode and grid through switch 8 or if preferred in series with a noninductive resistance 1'. Then the suprising prenomcnon appeared that the tube at once took up the saturation current of several hundred milliainperes, and this state of extraordinarily increased conductivity of the tube was maintained, when the switch 8 had been reopened. This condition with an ideally insulated auxiliary electrode between anode and cathode cannot be explgined by the characteristic curves of the tu e.

To examine this phenomenon, a circuit according to Fig. 3 was made in which an electrostatic voltmeter I with a very large resistance was inserted between grid and anode and a similar voltmeter II was inserted between grid and cathode. Now the above described experiments were repeated and at first a certain voltage Va was impressed betweeneathode and anode while switch 8 was opened.

The electrostatic voltmeter I now showed almost the total voltage Va whereas the voltmeter II indicated an indetectable voltage, as was to be expected, since almost the total potential goes normally along the discharge gap between anode and grid. When however the switch 8 was closed, the voltmeter I indicated the potential between grid and anode as practically 0, whereas the total voltage Va applied was indicated between cathode and grid by voltmeter II. The distribution of voltage in the first case is approximately illustrated by curve (Z, the distribution of voltage in the second case is approximately illustrated by curve e in Fig. 4, in which the ordinates are the length of the discharge gap and the abscissa is the voltage.

A probable physical explanation of this phenomenon has been found in the fact that i even an instantaneous suppression of a potential difference between anode and grid at the moment of inserting the condenser sufiices to efi'ect a permanent dislocation or disruption of the normal distribution of the field along the discharge gap.

Anyhow here is evidently the case of a total- I 1y novel physical fact in which the grid does not consume energy or reduce efficiency and yet takes up in a maintained state quite exceptionally high positive voltage dilferences as against the cathode and maintains the same.

Startin from this new basis applicants questioned whether it was possible to obtain the identical permanent final state by any method other than the switching in and out of a condenser. Consequently in a circuit according to Fig. 2 the switch .9 was constantly kept closed so that a constant either purely capacitative or a combination of capa-citative and resistance connection exists between grid and anode. \Vhen the voltage Va was increased it was found that when passing through a certain value of voltage the same phenomenon of disruption of the field occurred, i. e., the sudden and discontinuous decrease of the inner resistance.

Fig. 5 shows diagrammatically the qualitative variation of the inner resistance of a discharge gap in accordance with the theories of the invention wherein the ordinate is the inner resistance Re and the abscissa is the volt- '2 to value 3. When further-increasing the anode voltage applied, it increases owing to the limitation of the current by its saturation value, gradually in the direction of value 4-. The dotted curve would indicate the normal Variation at the inner resistance to be expected according to the former state of scientific theory.

The experiments have shown that the reduction of the resistance takes place practical- 1y instantaneously and is therefore a discontinuous or unstable variation of the value of the inner resistance. This upsetting of resistance may even take place in a practically intinitely short time.

Instead of the over-bridging elements placed betweenthe auxiliary electrode and the anode it is possible furthermore to apply a correspondingly high voltage between the auxiliary electrode and the cathode or a correspondingly low voltage between the auxiliary electrode and anode, and produce the same phenomenon. Also the employment of a magnetic influence on at least a part of the discharge gap may produce a similar etl'ect, i. e., the phenomenon of disruption.

A further invention in reference to the dis charge gap which is influenced in the way described is the generation of oscillations by this means.

A suitable circuit is illustrated diagrammatically in Fig. 6 omitting means for transferring the efi'ect to an antenna. There are also omitted all possible modes of controlling the generated alternating currents by the human voice (telephony) or by notes (tone transmission) or by keying (telegraphy).

In this circuit diagram of Fig. 6 the discharge gap In, a is connected with an oscillatory'system consisting of the combination or a self inductance L and a capacity C, or rather, it forms part thereof. It is an operating resistance, in which the generated alternating current of high frequency is consumed. The direct current required to feed the oscillatory system is applied by inserting one or several stabilizing choke coils (l at the main electrodes of the discharge gap.

Before explaining the method of operation of this circuit it is necessary to state that this is only one instance of the many possible ways. One may employ also any combination in parallel of self inductance and capacity or a combination in parallel and in series. One

4 may also provide any intermediary circuit or fiy wheel circuit. The oscillations generated must not necessarily be led to an antenna but.

may be employed for any other purpose e. for superim osedreceivmg. Although in t e following t e generation of oscillations for such purposes described, the invention is by no means restricted thereto.

In the circuit diagram of Fig. 6 the auxiliary electrode 9 is connected by means of a switch a with the resistance r and condenser c in series in the same manner as in Fig. 2. In order to'maintain oscillations it is sufticient to employ condensers or resistances or self inductances alone in this place. It has even been proved that the state of generation of oscillations may also be. attained when all circuit connections between grid and anode are omitted, especially if by suitable dimensioning sufiicient inner capacity exists inherently between the auxiliary electrode and one of the main electrodes. e

A state of oscillation is also obtainable by employing a graphite resistance as a connection between grid and anode. This is undoubtedly a proof that the connection between grid and anode employed for initiating or maintaining oscillations need not be oscillatory or tunable.

The generation of continuously undam ed alternating currentsup to the highest ii'equencies with constant amplitude b means of the circuit according to Fig. 6 wil be next explained. Assume that the amplitude of the alternating current generated is equal to or greater than the direct current value of the supply current and therefore oscillations of this new kind are generated. As a characteristic of these, it is well known that the current going through the discharge gap becomes periodically practically 0 or at least comparatively small relative to the current values during the remaining period of oscillation.

Assuming that in the circuit according to Fig. 6 a. direct current voltage is applied to the discharge gap,smaller than the disruption voltage characteristic of this discharge gap, the latter passes according to the above explanation only a very small current. Now the ca. pacityCintheoscillatingcircuit, having been charged to a potential greater than the disruption voltage of the tube, is suddenly applied to the tube or the discharge gap, the limitingvalue of disruption voltage of'the discharge gap is thereby suddenly exceeded and practically instantaneously there occurs the disruption of the field distribution along the discharge gap, i. e., the inner resistance decreases to such an extent that the capacity discharges at once through the discharge gap, the self inductance L and so on. The discharge, however, becomes interrupted at the very movement when the discharging current which is of course alternating becomes opposed to and equal to the direct current going through the discharge gap.

only a part of the resistance variable.

In consequence of the valve effect of the discharge gap a further flow of current through the discharge gap is impossible and now commences an interval during which the direct current supply stabilized by the choke coils D charges anew ,the capacity C of the oscillatory system according to the theory the voltage at the capacity rises from a negative value in an approximately straight line reaching ultimatel at the end of the charging interval to sue 1 a positive voltage value as corresponds with the disruption voltage of the discharge gap so that again a sudden decrease of resistance occurs in the tube and a fresh process of discharging commences.

This process is diagrammatically illustrated in Fig. 7, in which the abscissa 23 gives the time and the ordinates shows the direct current supply rig and the alternating discharge current 2'.

Characteristic of this new circuit for generating continuous alternating currents is particularly the fact that no noticeable tension occurs between the auxiliary electrode and anode during the real operating inter.- val of the discharge gap. During this interval the capacity C discharges via the discharge gap, whereas during the interval of inactivity of the discharge gap, during which the capacity C is charged from the supply source, there is no noticeable diflerence of potential between the auxiliary electrode and the cathode.

In consequence of the sudden variation of resistance in the discharge gap one has to deal with a kind of interruption phenomenon and there is so to speak a periodic swinging back and forth between two diiferent complexes of phenomena within the discharge gap, This is specially favorable for purposes of wireless high speed telegraphy since in a circuit arranged according to this invention the oscillation start instantaneously and not gradually, as in the old systems. At high speed sending gradual starting of oscillations may cause indistinctness of signals, while according to the above theory the magnitude of discharges is the same during the first cycle as during any subsequent cycle.

Further experiments with the invention have proved that at a certain supply voltage in the discharge gap and a certain construction and arrangement of the electrode 9 just the passage through a certain resistance value 1 produces the disruption. It is therefore not necessary to make variable the whole of the resistances overbridging a part of the discharge gap. A part may be constant and This variation causes the passage through the disruption voltage. The described small variable balance of resistance may even take over the function of the switch 8 (Fig. 6). This arrangement therefore oifers the possibility of distant control, with the circuits on the anode side used as repeaters to operate instruments or relays of higher current values. In order to obtain the highest possible sensitiveness of the switch controlled from a distance or of the variable resistance taking the place of the switch for the production of the disruption phenomenon, it may be desirable to choose besides a definite magnitude of resistance also a definite heating current for the filament and a definite disruption voltage I). By adjusting either of these values one may approach as near as desired to the disruption point 2 of the disruption curve (Fig. 5) so that a slight'variation of resistance or closing of the switch suffices to produccthe disruption phenomenon with any desired sensitiveness.

Fig. 8 shows the method of connection in which a special variable resistance is connected in series with one or more constant and usually high ohmic resistances o. In this example this variable resistance consists of a controlled discharge gap with anode n, grid 73 and cathode t; this discharge gap may be of the gas ionization, or of the electron discharge, or of the thermionic discharge type, and have a liquid or a solid cathode. In Fig. 8 a glow cathode is provided. Between grid 1' and cathode t is provided a double pole switch a, by means of which in the dotted position a negative potential is applied to the grid 2' whereas in the full line position a positive potential is connected to the grid 2'. In the full line position the inner resistance of the gap, anode n-cathode 23, becomes considerably reduced and thereby a part of the discharge gap ak is over-bridged in such a way that its inner resistance is suddenly and considerably changed. By moving the switch a to the dotted position the state of increased conductivity of the discharge gap al is ended.

The controlled discharge gap nt operates in this case similarly to a switch. By suitably choosing it as well as the series resistances 0, the disruption of the field of the voltage along the discharge gap ala may be assured for any value of voltage applied to this gap by a corresponding control of the gap nt.

Instead of adjusting the resistances 0, to secure the maximum sensitiveness of the auxiliary gap the same result may be obtained by applying a suitable constant biasing potential for this purpose.

If it is undesirable to have a continuous high absorption current by the tube or to employ in order to prevent this current special means such as switching off the supply source or reducing the heating. then it is advisable to use pulsating direct current or alternating current supply. For this )urpose any suitable supply source may e employed. It will however be found that, irrespective of the supply, it is particularly simple to employ the discharge for generation of oscillations.

It is thus possible to develop a circuit according to ig. 9, differing from that of Fig. 8 only by the insertion of a series combination of self induction Z and capacity p in parallel with the supply source I), together with intermediary stabilizing choke coils (Z. By adjusting the values Z or p the number of oscillations of this arran ement is controllable. If with a suitable 0 mice of overbridging elements the switch a is brought into the fu 1 line position shown in Fig. 8, the starting of oscillations may be noticed; if the switch u is brought into the position indicated by dotted lines, the oscillations are interrupted. This is evident since the falling alternating voltage of the oscillation passes the value of the disruption voltage, thereby producing the normal state of reduced conductivity. This is then maintained in consequency of changing over the switch u. The oscillating state is thus blocked. By suitable adjustment of the voltage I), it is possible to have a condition with the switch u in dotted position just below the limit of starting of oscillations, and therefore a slight increase of voltage between'grid i and cathode t by switching over the switch u sufiicies to start the continuous state of oscillations.

Experiments have proven that when an oscillatory circuit is connected with the disruption tube and continuous oscillations generated in this circuit, with proper adjustment of the resistance and of the switching tube, an influencing of these oscillations in accordance with speech will take place if the microphone is applied to the grid-cathode gap of the switching tube. In such a way telephone signals may be transmitted with or without wires. By the variation of resistance in the disruption circuit the disruption voltage is varied within certain limits shortening or lengthening thereby the charging impulses of the capacity in the oscillating circuit, or causing the oscillations to start when speaking to the microphone and to cease when leaving off speaking. But this takes place without thereby precluding the telephonic influence.

Fig. 10 shows one method of constructing such telephonic circuit. The switching tube 'nz't is inserted, if desired in series with a resistance 0, between anode a and grid 9 of the main tube. In parallel with anode acathode is (theheating current of which may be adjustable) is again the series combination of self inductance Z and capacity p. The grid circuit 5-16 of the switching tube is directly or indirectly influenced by a microphone m. The resistance anode n-cathodc t, of the switching tube is thereby influenced according to the speech. This variation of resistance of the switching tube varies the disruption voltage in the above described manner and produces thereby a telephonic influence. The modulated high frequency waves may be transmitted, e. g., by wireless by ltd coupling a transmitting antenna h by means of self inductance Z; instead of a transmitting antenna for space waves a couplin element may be provided which transfers t e generated waves to wires gvired wireless) or finally a wire line may e coupled by means of self inductance Z, giving ordinary wire telephony.

It is of course possible to obtain superimposed reception by causin the incoming high frequency waves to inter ere with the somewhat different local high frequency wave, this local wave being generated-by a method similar to that, e. g., which has been described in connection with Figs. 6 and 7.

What we claim is:

1. In an oscillating system including a discharge tube having a filament, a grid and a plate, said tube having a normal inner resist: ance between said filament and plate, an impedance, means for Varying the impedance, and circuit connections from the impedance to the grid and plate whereby a gradual variation of said impedance abruptly varies the normal inner resistance of the tube.

2. In an oscillating system includin a three element discharge tube, including a filament, grid and plate and having a characteristic curve in which an abrupt change in the inner resistance of the tube occurs at a predetermined value of grid and plate potentials with respect to the filament, a first resistance, a variable resistance connected between grid and plate elements of the tube, and a source of energy for heating the filament to-produce a normal current flow between said plate and filament elements, the method of controlling the electronic discharge characteristic which comprises adjusting the average value of the variable resistance to produce a grid potential near the value at which the abrupt change in inner resistance occurs and varying the first resistance to change the inner tube resistance to pass through the abrupt change value.

3. In combination, a three element discharge tube having a characteristic such that an abrupt change in inner tube resistance occurs at a predetermined potential of one tube element with respect to another one of the tube elements, a source of energy having a potential near the said predetermined potential Value of said tube, said source of energy being applied to said two tube elements, the potential of which is controlled by said source of energy and connected to said two tube elements for changing the potential-of the one tube element with respect to the other to the predetermined value and a source of signalling energy connected to the one element and a third of said elements for controlling the tube currents resulting from the abrupt change in resistance.

4. In combination with a three element discharge tube, provided with a filament, grid and plate and having a characteristic such that at a predetermined potential of the plate with respect to the filament of the tube there is an abrupt change in the inner resistance of the tube, a source of energy having a potential value near the predetermined potential, said source of energy being applied between said plate element and filament element, electrostatic and electromagnetic means connected to said source of ener for formin an oscillatory circuit, said oscillatory circult bein connected to the plate of said tube for app ying the predetermined potential thereto during certain parts of each oscillation and an input circuit connected between the plate and the third element for modulating the oscillations in said oscillatory circuit.

5. In combination, a three element discharge tube, provided with a filament, grid and plate and having a characteristic such that at a predetermined grid and plate potential there is an abrupt change in the inner resistance of the tube, a source of energy having a potential value near said predetermined potential of said tube, said source of energy being applied the plate and filament, electrostatic means connected to said source of energy, means whereby the electrical potential of said electrostatic means is changed to the predetermined grid and plate potential, said electrostatic means being connected to the filament and plate elements of said tube for applying the predetermined potential thereto, circuit connections whereby said electrostatic means discharges the energy stored therein in response to a change of inner tube resistance whereby-the potential applied to the plate and grid of the tube is changed from the disruption value to a different value and an input circuit connected to the grid element for controlling the operation of the tube.

6. The combination with a three element tube, provided with a filament, grid and plate and having a characteristic such that at a predetermined potential of the plate with respect to the filament there is an abrupt change in the inner resistance of the tube, of a source of energy having a potential value less than said predetermined value of the tube, a condenser, circuit connections from said source of energy to said condenser whereby the potential of said condenser is changed to a potential greater than the predetermined potential of said plate and circuit connections from said condenser to said plate and filament elements of said tube whereby the potential of the plate of said tube is raised to the predetermined potential, an input circuit connected to the grid element and means in said input circuit for controlling the operation of said tube.

7. In a combination comprising a three element tube having a characteristic such that a predetermined potential of the plate with respect to one of the elements there is an abrupt change in the inner resistance of the tube, a source of energy havin a potential value near said predctermine value of the plate of the tube, a condenser and circuit connections from the source of energy to two of the tube element and to the condenser, the method of operating the tube which comprises charging the condenser from the source of energy to a potential equal to the predetermined value of the tube, raising the potential of the element to which the condenser is connected to the predetermined value, by the increased potential of the condenser, discharging the condenser during the resultant increased current flow in the tube due to the abrupt change in resistance of the tube and variably controlling the potential between the third element and one of the two other elements of the tube to control the operation of said tube.

8. In a combination of a three element tube provided with a grid, filament and plate and having a characteristic by virtue of a relatively large positive potential applied to the grid with respect to the filament such that at a predetermined potential of the plate with respect to another of the elements there is an abrupt change in the inner resistance of the tube, with a source of energy having a potential value near said predetermined potential value of the plate of the tube, a condenser, circuit connections from the source of energy to the plate and to the condenser, and input circuit connections to the grid, the method of generating oscillations which comprises charging the condenser from the source of energy to the predetermined potential of the plate, raising the potential of the plate by the charged condenser to the predetermined value, discharging the, condenser during the abrupt increased current flow of the tube due to the abrupt change in resist ance, thereupon repeating this cycle and varying the produced oscillations by currents over the input circuit connected to the grid.

9. In a combination including a three element tube provided with filament, grid andplate, means for applying a relatively large positive potential to the grid with respect to the filament whereby the tube has a characteristic such that at a predetermined po tential of the plate with respect to one of the elements there is an abrupt change in the illner resistance of the tube, a source of energy having a potential value near said predetermined potential value of the plate, a condenser, circuit connections from the source of energy to the plate and to the condenser and input circuit connections to the grid, the method of generating oscillations which comprises charging the condenser from the source of energy to the predetermined plate potential, raising the potential of the plate by the charged condenser to the predetermined value and discharging the condenser during the increased plate, current flow due to the abrupt change in inner resistance of the tube, thereupon repeating this cycle, and modulating the generated oscillations in accordance with signalling frequencies in the input circuit connection to the grid.

10. The method of operating a three element discharge tube by means of an electrical device and an external impedance connected to the filament and plate elements of the tube and a second impedance connected to the grid and plate elements which comprises producing abrupt changes in the inner resistance of the tube in response to gradual variations of the potential across the first impedance and modifying the currents flowing as a result of the change in tube resistance in accordance with the current flowing over the second impedance.

11. In a three element tube provided with a filament, grid and plate, means for applying a relatively large positive potential to the grid with respect to the filament, devices including an impedance connected to filament and plate elements to control the inner resistance of the tube, and a device connected to the grid element, the method of operating the tube which comprises producing abrupt changes in the inner resistance of the tube in response to gradual variations of the potential across the external impedance and mod ulating the resulting currents flowing by currents in the device and circuit connection to the grid element.

12. In a three element discharge tube provided with a filament, grid and plate, and means for applying a relatively high positive potential to the grid with respect to the filament whereby the tube has a characteristic such that an abrupt change in inner resistance of the tube occurs at a predetermined value of resistance, the method of operating the tube which comprises normally maintaining the inner resistance of the tube close to the value at which an abrupt change in inner resistance occurs and varying the inner resistance from said normal maintained value to the predetermined value.

13. In a three element tube having a point at a predetermined inner resistance at which an abrupt change in resistance occurs, and an input circuit connected to said tube, the method of transmitting signals which comprises generating oscillations by varying the inner resistance of the tube over resistance values including the predetermined resistance and modulating the generated carrier current in accordance with signals in the input circuit.

In testimony whereof we afiix our signatures.

LUDWIG KUHN. KARL ROTTGARDT. 

